Process for preparing a soft and tenacious nonwoven fabric

ABSTRACT

A PROCESS FOR PREPARING A NONWOVEN FABRIC COMPRISING FORMING A UNIFORM MAT OF FIBERS FROM 1/2 TO 5 INCHES IN LENGTH AND FROM 0.5 TO 10 IN DENIER, NEEDLE-PUNCHING SAID MAT FROM 600 TO 6000 TIMES PER SQUARE INCH BY MEANS OF A NEEDLE LOOM PROVIDED WITH FELTING NEEDLES OF FROM NUMBER 30 TO NUMBER 46 TO THEREBY FORM A FIBER SHEET HAVING A WEIGHT OF AT LEAST 150 G./M.2 AND AN APPARENT DENSITY OF AT LEAST 0.15, IMPREGNATING SAID SHEET WITH A BONDING AGENT LIQUID COMPRISING AN ANIONIC LATEX OF A HIGH MOLECULAR WEIGHT ELASTIC MATERIAL, A NONIONIC SURFACE ACTIVE AGENT HAVING A HLB OF AT LEAST 11 AND A CLOUD POINT OF FROM 30 TO 85*C., AND, AS AN INDISPENSABLE COMPONENT, IF THERE IS NO PROTECTING EFFECT OF SAID SURFACE ACTIVE AGENT, AN IONIZABLE ORGANIC OR INORGANIC METALLIC SALT TO COAGULATE SAID LATEX, WHEREIN THE CONTENT OF SAID HIGH MOLECULAR WEIGHT ELASTIC MATERIAL IS AT LEAST 10% BY WEIGHT OF THE TOTAL WEIGHT OF SAID BONDING AGENT LIQUID, WHEREIN THE CONTENT OF SAID NONIONIC SURFACE ACTIVE AGENT IS FROM 5 TO 30 PARTS BY WEIGHT, PER 100 PARTS BY WEIGHT OF SAID HIGH MOLECULAR WEIGH ELASTIC MATERIAL, AND WHEREIN THE AMOUNT OF SAID METALLIC SALT IS SUFFICIENT TO COAGULATE SAID HIGH MOLECULAR WEIGHT MATERIAL, SO AS TO DEPOSIT FROM 20 TO 50 PARTS BY WEIGHT OF SAID HIGH MOLECULAR WEIGHT MATERIAL PER 100 PARTS BY WEIGHT OF FIBER COMPONENT; ELEVATING THE TEMPERATURE OF SAID IMPREGNATED BONDING AGENT LIQUID TO A TEMPERATURE ABOVE ITS COAGULATION TEMPERATURE TO THEREBY COAGULATE SUBSTANTIALLY ALL OF SAID HIGH MOLECULAR WEIGHT MATERIAL WITHOUT MIGRATION IN THE DIRECTION OF THE SHEET THICKNESS.

United States Patent O 3,669,784 PROCESS FOR PREPARING A SOFT ANDTENACIOUS NONWOVEN FABRIC Tadashi Yokota, Kyoto, and Taizo Asai, Otsu,Japan,

assignors to Nippon Cloth Industry Co., Ltd., Ukyoku, Kyoto, Japan NDrawing. Filed Jan. 30, 1970, Ser. No. 8,097 Int. Cl. B32b 35/00 U.S.Cl. 156-148 15 Claims ABSTRACT OF THE DISCLOSURE A process for preparinga nonwoven fabric comprising forming a uniform mat of fibers from /2 to5 inches 1n length and from 0.5 to in denier, needle-punching said matfrom 600 to 6000 times per square inch by means of a needle loomprovided with felting needles of from number 30 to number 46 to therebyform a fiber sheet having a Weight of at least 1.50 g./m. and anapparent density of at least 0.15, impregnating said sheet with abonding agent liquid comprising an anionic latex of a high molecularweight elastic material, a nonionic surface active agent having a HLB ofat least 11 and a cloud point of from 30 to 85 C., and, as anindispensable component, if there is no protecting effect of saidsurface active agent, an ionizable organic or inorganic metallic salt tocoagulate said latex, wherein the content of said high molecular weightelastic material is at least 10% by weight of the total weight of saidbonding agent liquid, wherein the content of said nonionic surfaceactive agent is from 5 to 30 parts by weight, per 100 parts by weight ofsaid high molecular weight elastic material, and wherein the amount ofsaid metallic salt is suflicient to coagulate said high molecular weightmaterial, so as to deposit from 20 to 50 parts by weight of said highmolecular weight material per 100 parts by weight of fiber component;elevating the temperature of said impregnated bonding agent liquid to atemperature above its coagulation temperature to thereby coagulatesubstantially all of said high molecular weight material withoutmigration in the direction of the sheet thickness.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to a process for preparing a soft and tenacious nonwoven fabrichaving excellent air and moisture permeability and one which isparticularly suited as a substitute leather or as a foundation thereof.

Description of the prior art Heretofore, various processes have beenemployed for preparing nonwoven material suitable for these uses. Amongthese processes, the following technique is known: needle-punching a matformed with fibers, impregnating the mat with a solution of a highmolecular weight elastic material in a solvent, dipping the mat into aliquid which is miscible with the solvent in the solution and which is anon-solvent for the high molecular weight elastic material to coagulatethe solution of the elastic material, thereby depositing a porous highmolecular weight elastic material on the fiber structure, andsubsequently, after extracting the solvent, drying the mat. However, ingen- "ice eral, this technique has the disadvantage that the solvent isexpensive and that a relatively long time is required vfor completelyextracting and removing the solvent.

Another known process comprises impregnating a fiber mat with a latex ofa synthetic rubber of snythetic resin and then freezing it or treatingit with a liquid containing an agent which is capable of coagulating thelatex, and thereafter drying it. However, in the freezing method, theapparatus required for continuous freezing is not simple in structure,and in the method in which a coagulating bath is used, it is diflicultto coagulate an article uniformly and rapidly in the direction of itsthickness, especially when it has a relatively large thickness.

It is a principal object of the present invention to remedy theabove-mentioned disadvantages.

SUMMARY OF THE INVENTION According to the process of the presentinvention, the coagulation can be rapidly and completely carried out byusing a latex type of bonding agent. The nonwoven fabric prepared by thepresent process has the advantage that, even when the relatively thickfabric is in a stratified form, each layer of fabric has homogeneousproperties, since the porous high molecular weight bonding agent isuniformly distributed through the thickness of the fiber foundation.Further, the nonwoven fabric manufactured by the present process has asoft feeling as well as a high tear resistance, because the adhesion offiber and high molecular weight bonding agent is not in the form of areabonding, rather, in the form of point bonding.

The process of the present invention will be further illustrated below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present processcomprises: forming a uniform mat of natural fibers, regenerated fibers,synthetic fibers or mixtures thereof; passing the mat through a needleloom provided with felting needles of from number 30 to number 46, toform a sheet which has a punching density of from 600 to 6000 times persquare inch total; impregnating the sheet with a liquid bonding agentwhich has the following composition and properties: that is, anioniclatex or emulsion of synthetic rubber or elastic synthetic resin, anonionic surface active agent which is above 11 in HLB (HydrophileLipophile Balance; see Grifiin, W. C., Journal of The Society ofCosmetic Chemists, 311 (1947)) and has a cloud point (Cp) in the rangefrom 30 to C., and an inorganic or organic salt which is capable ofcoagulating the above-mentioned anionic latex if there is no protectingeffect of the nonionic surface active agent, the latex or emulsion beingabove 10% in solid concentration of the above high molecular weight(i.e., at least 10,000) bonding agent and having a viscosity of 10 to1000 cp.; placing the sheet into an atmosphere which is at a temperatureabove the coagulation temperature of the impregnating liquid and whichhas a relative humidity of above or into a hot water bath, orirradiating the sheet with a high frequency electric wave to rapidlyelevate the temperature to a temperature above the coagulationtemperature of the bonding agent liquid, thereby immediately eliminatingthe latex protecting action of the added nonionic surface active agentfor a metallic ion of the inorganic or organic salt, and, lastly,coagulating the high molecular weight elastic material to deposit itwithin the fibrous network structure, washing it with water and dryingit.

As a stock fiber used in the process of the present invention, anyconventional textile fiber can be used, however, it is necessary to usea fiber of from 0.5 to 10 in denier and from /2 to 5 inches in length.

If the needle punching density is below 600 times per square inch, it isdifficult to obtain the leather-like feeling which is the object of theprocess of the present invention, and as the needle punching density isincreased, the softness of the product is improved and a leather-likefeeling is obtained. This effect reaches the maximum point at a densityof about 6000 times per square inch, and a needle punching densitybeyond that is of no use and, in fact, is harmful since this decreasesthe strength of the product. -It is also necessary that the weight ofthe punched sheet be above 150 g./m. and above 0.15 in apparent density.

The latex of the high molecular weight bonding agent is required to beone in which an anionic surface active agent is used as a dispersingagent. To satisfactorily attain the rapid and efiective coagulation ofthe high mo- 1 lecular weight component in the wet heat treatment afterthe impregnation of the bonding agent liquid, which is the chiefcharacteristic of the present invention, the concentration of the highmolecular weight component contained in the bonding agent liquid must beabove If the concentration of the high molecular weight component in theimpregnating liquid is below 10%, it is not sufliciently coagulated bythe heat treatment since the amount of the bonding agent which is washedaway is rapidly increased and the remaining gel is semi-flowable, andthus, the desired effect of the present invention cannot be sufiicientlydisplayed.

Useful as a high molecular weight material for the bonding agent are,for example, polybutadiene, polychloroprene,a butadiene-acrylonitrilecopolymer, a butadienestyrene copolymer, polyurethane elastomer,polyacrylic acid ester resin, etc. Two or more of these anionic latexesmay be mixed together for use in the present invention. As a nonionicsurface active agent to be blended, the following are suitable: anethylene oxide-propylene oxide copolymer, sorbitane ester, fatty acidester, an ethylene oxide additive of an alkyl benzene acid, etc. whichhave a cloud point of from 30 to 85 C. and which are above 11 in HLB. Ifthe cloud point is within this range, the coagulation by heat treatmentis rapid and exact and the storage stability of the bonding agent liquidis good. If the HLB is above 11, the produced gel has a suflicienthardness and fills the fibrous network structure in the form of a porousbonding body; however, as the HLB is decreased below 11, the gel becomessemiflowable and, in the dehydrating step and drying step aftercoagulation, it moves easily and tends to become hard in feeling. Theamount of nonionic surface active agent is suitably more than 1% andpreferably from 5 to 30% by weight, based on the weight of highmolecular weight material.

In the preparation of the bonding agent liquid, the above nonionicsurface active agent is first added to a latex of the bonding agent highmolecular weight material and, after suficient stirring by means of ahigh speed stirrer such as a propeller mixer,- homogenizing mixer, etc.to form a protecting colloid of dispersed high molecular weightparticles, a metallic salt is added thereto.

Suitable as a metallic salt for coagulation are, for example, sodiumsalt, potassium salt and aluminum salt of sulfuric acid, nitric acid,acetic acid, etc., calcium chloride, and alums which, when theabove-mentioned nonionic surface active agents has no protecting action,is capable of coagulating the above-mentioned anionic latex or emulsion.

The amount of bonding agent liquid to be impregnated is suitably such anamount that the content of high molecular weight solid to be adhered is20 to 250 parts,

by weight, per 100 parts, by weight, of fiber. As a heat medium used inthe heat treatment of the impregnated sheet with the above mentionedheat sensitive bonding agent liquid, heated and dried air is notsuitable because its heat capacity and heat conductive coefiicient aresmall and the surface of the sheet is dried. In order to conduct rapidheating while preventing the drying of the water content, theimpregnated fiber sheet is placed in hot water at a higher temperaturethan the coagulation temperature of the bonding agent liquid, or in asuperheated saturated vapor, or in air at a temperature of above C. andat a relative humidity of above and thereby, uniform and rapidcoagulation becomes possible. The same effect can be attained byemploying high frequency heating without using these heat conductivemedia.

Thus, the sheet impregnated by the coagulation treatment is thendehydrated to remove some isolated water and, even if dried, canmaintain the bonding state existing at the time of coagulation withoutthe movement of bonding agent within the structure of the nonwovenfabric occurring. In general, the nonionic active agents and metallicsalts are preferably removed by washing with water before drying, sinceleaving these materials within the nonwoven fabric is useless and isoccasionally harmful for some uses.

According to the process of the present invention as described in detailabove, a nonwoven fabric having excellent natural leather-like feeling.and strength can be produced by needle punching a web and thesynergistic effect of a limited impregnation of bonding agent and acoagulation treatment. Further, according to the process of the presentinvention, since the high molecular weight bonding agent does not movewithin the fiber structure of the nonwoven fabric in the manufacturingstep but is uniformly distributed and adhered throughout the thicknessof the nonwoven fabric, a homogeneous nonwoven fabric product can beobtained and efiicient production is possible, even when the product isdivided into layers.

The present invention will be further illustrated by the followingnonlimiting examples.

EXAMPLE 1 70 parts, by weight, of nylon fiber (2 denier, 51 mm.) and 30parts, by Weight, of rayon fiber (2 denier, 51 mm.) were blended andformed into a mat of about 900 g./m. in weight by means of a card and across folder, and then were passed through a needle loom provided withnumber 40 felting needles .to carry out punching of 2000 times per sq.in. total, from both sides, to obtain a sheet of about 750 g./m. inweight and about 4 mm. in thickness (that is, an apparent density ofabout 1.87). The composition of the bonding. agent liquid used forimpregnating this sheet was as follows:

Parts by weight AnlODlC butadiene acrylonitrile latex (trademark: Hycar1571; manufactured by Nihon Geon Co.,

Ltd.) Nonionic surface active agent, HLB 12, Cp 43 C.

(trademark: H28 208; manufactured by Niss Chemical Industry Co., 'Ltd.)5 CaCl;, 2 Water 30 dipping in a hot water bath of about 90 C. for 1minute, it was squeezed again by means of the squeezing roll. The latexwas thereby completely coagulated and, when being squeezed, thedischarged liquid was transparent. The impregnated sheet was washed withwater to remove the active agent and. CaCl and then dried to obtain adense sheet of about 48 mm. in thickness and about 1410 g./m. in weight.This sheet was divided into 6 sheets by means of a band knife commonlyemployed in the leather industry, each of which being 0.8 mm. inthickness, to obtain a flexible nonwoven fabr c having an excellentleather-like feeling, in which the adhering state of the bonding agentwas uniform on each of the 6 sheets, although both outside surfaces weresomewhat nappy.

EXAMPLE 2 The needle punched sheet used in Example 1 was impregnatedwith a bonding agent liquid having the following composition:

(trademark: Nonipol 85; manufactured by Sanyo Chemical Co., Ltd.) 1 Q1012 Water 25 The bonding agent liquid was prepared by the same method asin Example 1. The above-mentioned fiber sheet was impregnated with thisbonding agent liquid, squeezed to about 300% of liquid content, placedin a box at a. temperature of 98 0., into which superheated saturatedsteam was continuously blown, for about 1 minute, and squeezed by meansof a squeezing roll to remove water. Thereby, only the isolated waterwas removed and the latex was completely coagulated. The sheet wasfurther washed with water to remove the active agent and CaCl and thendried to obtain a dense sheet of about 4.5 mm. in thickness and 1520g./m. in weight. From both sides of the sheet were removed outsidelayers 0.25 mm. thick by the same method as in Example 1 and theremaining part was divided into 4 sheets, each of which was 1 mm. inthickness, to obtain 4 nonwoven fabrics, each of which had the feelingand strength suitable for a foundation of substitute leather and whichwas uniform in the adhered amount of bonding agent.

EXAMPLE 3 The sheet of Example 2, after having been impregnated with thebonding agent liquid, was cut into a piece of 30 x 30 cm., placed in anultra-short wave heating apparatus of 2.4 kw. in output, and treated byirradiation for 10 seconds, and then squeezed by the same roll as inExample 2 to remove water. The coagulation effect of the latex wasequivalent to that in Example 2.

What is claimed is: 1. A process for preparing a nonwoven fabriccomprisforming a uniform mat of fibers having a length of from about /zto 5 inches and a denier of from about 0.5 to

forming a fiber sheet having a weight of at least about 150 g./m. and anapparent density of at least about 0.15 by needle-punching said uniformmat from about 600 to 6,000 times per square inch by means of a needleloom provided with felting needles of from about number 30 to aboutnumber 46;

impregnating said fiber sheet with from about 20 to 50 parts by weight,based on 100 parts by weight of fiber, of a high molecular Weight rubberor elastic synthetic resin by impregnating said fibrous sheet with aliquid bonding agent which consists essentially of:

(1) an anionic latex of said high molecular weight synthetic rubber orelastic synthetic resin, said latex being present in an amount of atleast about 10% by weight, based on the total weight of said liquidbonding agent;

(3) from about 5 to 30 parts by weight, based on the weight of said highmolecular weight synethetic rubber or elastic synthetic resin, of anonionic surface active agent having a Hydrophile Lipophile Balance ofabove 11 and a cloud point of from about 30 to C.; and

( 3) an amount of an inorganic or organic metallic salt sufiicient tocoagulate said anionic latex when the nonionic surface active agent nolonger surrounds and protects the particles of said anionic latex frombeing attacked by cationic metal ions from said metallic salt;

(4) rapidly elevating the temperature of the resulting impregnated fibersheet to a temperative above the coagulation temperature of said anioniclatex and depositing said high molecular weight synthetic rubber orelastic synthetic resin within the fibrous network of the impregnatedfiber sheet by coagulating said anionic latex;

(5) washing the resulting sheet with water; and

(6) drying the resulting sheet.

2. A process for preparing a nonwoven fabric as in claim 1, wherein saidfibers comprise polyamide fibers.

3. A process for preparing a nonwoven fabric as in claim 1, wherein saidfibers comprise polyester fibers.

4. A process for preparing a nonwoven fabric as in claim 1, wherein abutadiene-acrylonitrile copolymer is used as the high molecular weightmaterial.

5. A process for preparing a nonwoven fabric as in claim 1, wherein abutadiene-styrene copolymer is used as the high molecular weightmaterial.

6. A process for preparing a nonwoven fabric as in claim 1, wherein apolyurethane elastomer is used as the high molecular weight material.

7. A process for preparing a nonwoven fabric as in claim 1, wherein thetemperature of said impregnated fiber sheet is elevated by immersingsaid sheet in hot water.

8. A process for preparing a nonwoven fabric as in claim 1, wherein thetemperature of said impregnated fiber sheet is elevated by the action ofheated water vapor.

9. A process for preparing a nonwoven fabric as in claim 1, wherein thetemperature of said impregnated fiber sheet is elevated by the action ofhigh frequency dielectric heating.

10. The process of claim 1 wherein said high molecular weight syntheticrubber or elastic synthetic resin has a molecular weight of at leastabout 10,000.

11. The process of claim 1 wherein said liquid bonding agent has aviscosity of from about 10 to 1,000 centipoises.

12. The process of claim 1 wherein said high molecular weight syntheticrubber or elastic synthetic resin is selected from the group consistingof polybutadiene, polychloroprene, a butadiene-acrylonitrile copolymer,a butadiene-styrene copolymer, a polyurethane elastomer, a polyacrylicacid ester resin and mixtures thereof.

13. The process of claim 1 wherein said nonionic surface active agent isan ethylene oxide-propylene oxide copolymer, a sorbitane ester, a fattyacid ester or an ethylene oxide additive of an alkyl benzene acid.

14. The process of claim 1 wherein said metallic salt is a sodium,potassium, aluminum or calcium salt of sulfuric acid, nitric acid oracetic acid or alum.

15. The process of claim 1 wherein the temperature of said impregnatedfiber sheet is rapidly elevated by plac- 8 ing the impregnated fibersheet in air having a temperature 3,477,898 11/ 1969 Buif et a1. 156148X of above 80 C. and a relative humidity of above 90%. 3,321,356 5/1967Merriman et a1. 156148 X References Cited CARL D. QUARFORTH, PrimaryExaminer UNITED STATES PATENTS 5 G. G. SOLYST, Assistant Examiner3,383,273 5/1968 Pearson et al. 156-448 X 3,067,483 12/1962 Hollowell156148 X 3,336,173 8/1967 Renfroe 156--148 156306, 308

